Hydraulic jet method of drilling a well through hard formations



june 13, 1967 R,J GOODW1N ET AL 3,324,957

HYDRAULC JET METHOD OF DRILLING A WELL THROUGH HARD FORMATIONS Filed Sept. 24, 1965 8 Sheets-Sheet 1.

June 13, 1967 R. J. GQODWIN ET AL 3,324,957

HYDRAULIC JET METHOD OF DRILLING A WELL THROUGH HARD FORMATIONS Filed Sept. 24, 1965 8 Sheets-Sheet 2 TTOR/VEK Jun@ l3, i957 R. J. GooDwiN ET AL 3,324,957

HYDRAULIC JET METHOD Ol DRLLING A WELL THROUGH HARD FORMATIONS Filed Sept. 24, i965 8 Sheets-Sheet Z Jlm@ 13, 196? R, J, (300m/WN ET Al. 3,324,957

ULIC JET METHOD OF DRLLLINL, A WELL 1 N VEN TORS june i3, 1967 R` J, GOODWIN ET Al. 3,324,957

HYDRAULIC JET METHOD 01 DRILLING A WELL THROUGH HARD FORMATIONS Filed Sept. 24. 1965 a sheets-sheet INVENTOR5. A705597' J. GOOM//V ERNEST. MOP, JOSEPH L PEKAREK, PAL/l. MII .SCHUB .Hume 13, 1967 R. J. GQODWIN ET AI- 3,324,957

HYDRAULIC JET METHOD O1" DRILLING A WILLL v THROUGH HARD FORMATIONS Filed Sept. 24, 1963 8 Sheets-Sheet 6 N VENTORS.

Fig 25 ATTO/VEV.

June ls, 1967 R. J, GOODWIN ET AL 3,324,957

HYDRAULIC JET METHOD Of" ORILLING A 'HOLL THROUGH HARD FORMATIONS Filed Sept. 24, 1963 8 Sheets-Sheet 7 June L3, 1967 Q J, GOODW|N ET AL 3,324,957

, HYDRAULIC JET METHOD OF DHILLINO A WELL THROUGH HARD FORMATIONS 8 Sheets-Sheet 8 Filed sept. 24, 1955 ///5 il; m h u BY AND R United States Patent O "ice 3,324,957 HYDRAULIC JET METHOD OF DRILLING A WELL THROUGH HARD FORMATIONS Robert J. Goodwin, Oakmont, Ernest A. Mori, Hampton Township, Allegheny County, Joseph L. Pekarek and Paul W. Schaub, Penn Hills Township, Allegheny County, and' Robert E. Zinkham, Harrison Township, Allegheny County, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Filed Sept. 24, 1963, Ser. No. 311,034 2 Claims. (Cl. 175-67) This invention relates to the art of drilling deep boreholes in the earth and in particular concerns a drill bit employing hydraulic jets to perform substantially all of the rock-cutting action.

Conventional devices for drilling deep bore-holes function by making physical contact of the cutting surfaces of a metal drill bit with the rock formation at the bottom of the hole to mechanically cut the rock away. Such drill bits as the well known fish-tail bit, drag bit, core bit, roller bit, cone bit, disk bit, etc., all operate to make hole by mechanically breaking up the rock at the bottom of the hole whence the cuttings are removed to the surface of the earth by means of a circulating fluid medium such as lair, foam, or drilling mud. In mechanically breaking up the rock it is inevitable that a substantial amount of wear and breakage also occurs to the cutting elements of such a drill bit, so that eventually the bit wears out and can no longer make hole. The drill stem must then be withdrawn from the hole, the bit replaced, and the bit stem with the new bit reinserted in the borehole. In drilling hard formations in a deep hole the time spent replacing conventional drill bits may exceed the actual drilling time on bottom, and this results in -a loss of eiliciency and very substantially increases the expense of the drilling operation.

Hydraulic jets have heretofore been included with conventional drill bits, but these jets have been for the purpose of keeping the cutting edges of the drill bit, or the rock surface being cut, free from mud and chips produced by the bit thereby to increase the efficiency of the mechanical cutters on the bit. However, such ancillary jets as have been employed with conventional rock bits have no effective cutting action when operated under the pressures normally employed for iiuid circulation in conventional mechanical drilling operations.

We have found that when hydraulic jets are operated at very high pressures so that extremely high velocities are attained by the emerging jet stream, the fluid jet is very effective in making hole even in hard rock. By omitting substantially all mechanical cutters from the drill bit there is obtained a bit that is substantially free of mechanical wear or breakdown. Accordingly when such a bit is used in the hole, it will remain effectiveY to make hole for a much longer period of time than a bit that includes mechanical cutting elements. Also due to the fact that the jets tear up the rock into very small fragments, the cuttings are more easily removed by the circulating fluid than are the larger cuttings made by conventional mechanical drill bits, Furthermore, because of the mechanical simplicity of such an all-jet bit, such bits are very sturdy and are also relatively inexpensive, thus resulting in a further sav' ing of drilling expense. ln addition when such bits are operated in accordance with this invention, they -are found to make hole at a much faster rate than conventional bits.

A further disadvantage of conventional mechanical bits which is overcome by this invention is that a mechanical bit requires substantial weight to be applied to the bit in order to make it cut the rock being drilled. It is well known that high bit weight results in faster drilling with 3,324,957 Patented June 13, 1967 a mechanical drill bit, but it is also known that high bit weights result in greater deviation from a straight hole, as well as greatly increasing wear on mechanical parts of a mechanical bit land thereby decreasing its life. By the use of the present invention the weight on the bit is reduced very substantially over that used in mechanical drilling with resulting improvement in hole straightness.

When using conventional mechanical drill bits, the drill stem is required to perform three functions, namely (l) serve as a conduit for the drilling fluid, (2) serve to apply weight to the drill bit, land (3) serve to apply torque to rotate the drill bit. The latter two of these functions are stringent requirements that dictate the use of heavy pipe made of expensive high-strength steel. By the use of the present invention the requirements of applying weight and torque to the drill bit are substantially eliminated, whereby it becomes possible to use lighter weight, inexpensive drill pipe. In the present invention the only important function of the drill pipe is to serve as a conduit for the high-pressure drilling fluid which in the substantial absence of other mechanical stresses is easily met.

We have found that when a plurality of hydraulic jet streams of extremely high velocity are rotated in a borehole, very effective cutting action is obtained even in hard rock. In contrast to prior-art drilling devices, the drill bit of this invention makes substantially no physical contact of the tool employed to produce the high-velocity hydraulic jets with the surfaces of the earth formation being drilled or bored. Thus the drill bit of this invention is substantially free of the wear or breakdown occasioned by the physical contact of prior-art bit surfaces with the rock formation being drilled.

Although we have for convenience herein used the term bit to describe the drilling tool of the present invention, from the foregoing and the detailed description which follows it will be apparent to those skilled in the art that the process and apparatus Aof the present invention are entirely different from prior-art drill bits. A distinction is made between prior-art drill bits which are of the mechanical type wherein the rock-cutting action results from physical contact of the metal bit surfaces with the rock lformation at the bottom of the hole, and fthe jet bits of this invention wherein the rock-cutting action results from the erosive action of a high-velocity jet stream issuing from a nozzle thatV does not contact the rock formation, and as will become evident, functions most advantageously when the nozzle is spaced a specied distance (called Ithe standoff) from the rock being drilled or bored. Physical contact of the jet bits of this invention with the bottom of the hole is used only as Ia means to maintain standoff of the nozzles during rotation of the bit,

Accordingly, it is an object of this invention to provide a method of drilling capable of rapidly making hole and which employs high-velocity hydraulic jets to disintegrate the rock to be penetrated.

Another object of this invention is to provide a method of 'drilling that is highly effective in cutting hard rock without the use of mechanical cutters.

Another object of this invention is to provide a method of drilling employing high-velocity hydraulic jets and which drills a pilot hole that is subsequently enlarged to gauge.

These and other useful objects are attained by the invention described in this specification with reference to the accompanying drawings forming a part thereof, and in which:

" FIGURE 1 is a bottom view of one embodiment of the ldrill bit useful in this invention;

-FIGURE 2 `is la front elevation of one embodiment of the drill bit useful in this invention as viewed from the bottom of FIGURE l;

FIGURE 3 is a side elevation of one embodiment of the drill -bit useful in this invention as viewed from the right side of FIGURE 1;

FIGURE 4 is a cross section of the drill bit of FIG- URES 1 to 3 taken on the plane IV-IV of FIGURE l;

FIGURE 5 is a cross section of the drill bit of FIG- URES 1 to 3 taken on the plane V-V of FIGURE 1;

FIGURE 6 is a partial cross section of the drill bit of FIGURE 1 showing details of the end structure of the bit;

FIGURE 7 is a bottom view partly in section of the drill bit of FIGURE 1;

FIGURE 8 is a bottom view of a second embodiment of a drill bit useful in this invention;

FIGURE 9 is a front elevation of the second embodiment of this invention as viewed from the bottom of FIGURE 8;

FIGURE 10 is a side elevation of the second embodiment of a drill bit useful in this invention as viewed from the right side of FIGURE 8;

FIGURE 11 is a side elevation of the second embodiment of ya drill bit useful in this invention as viewed from the left side of FIGURE 8;

FIGURE 12 is an oblique elevation partly in section of the second embodiment of a drill bit useful in this invention as viewed from the lower right-hand corner of FIGURE 8;

FIGURE .13 is an oblique elevation partly in section of the second embodiment of a drill bit useful in this invention as viewed from the upper left-hand corner of FIGURE 8;

FIGURE 14 is a longitudinal cross section taken at the plane XIV-XIV of FIGURE 8;

FIGURE 15 is a partial longitudinal section taken at the plane XV-XV of FIGURE 8;

FIGURE 16 is a parti-al longitudinal section taken at the plane XVI- XVI of FIGURE 8;

FIGURE 17 is a partial longitudinal section taken at the plane XVII- XVII of FIGURE 8;

FIGURE 18 is a partial transverse cross section taken at the plane XVIII- XVIII of FIGURE 12;

FIGURE 19 is a partial transverse section taken at the plane XIX-XIX of |FIGURE 13;

FIGURE 20 is a partial transverse section taken at the plane XX--XX of FIGURE 13;

FIGURE 2l is a partial transverse section taken at the plane XXI-XXI of FIGURE r13;

FIGURE 22 is a bottom view of a third embodiment of a drill bit useful in this invention;

FIGURE 23 is a top view of the third embodiment of a drill bit useful in this invention;

FIGURE 24 is a side elevation of the third embodiment of a drill bit useful in this invention as viewed from the right side of FIGURE 22;

FIGURE 25 is a side elevation of the third embodiment of a drill bit useful in this invention as Viewed from the left side of FIGURE 22;

FIGURE 26 -is a section taken generally at the plane XXVI-XXVI of FIGURE 22; and

FIGURE 27 is a section taken Iat the plane XXVII- XXVII of FIGURE 22.

We have found that a hydraulic jet is substantially ineffective in cutting or drilling rock at low jet velocities, but at velocities exceeding a critical minimum cutting velocity the cutting rate increases rapidly with increasing jet velocity. In this invention the jet velocity exceeds the critical minimum cutting` velocity and by the term high-velocity jet as used herein is meant a jet whose velocity exceeds the critical minimum cutting velocity. Inasmuch as the jet velocity for duid of constant density is uniquely dependent on the pressure of the fluid applied to the nozzle, it is further to be understood that the pressure inside the bit exceeds the external ambient pressure by an amount sufficient to effect at the exit of the nozzle or nozzles a jet stream whose velocity exceeds the critical minimum cutting velocity for the rock or target being drilled and for the particular drilling liuid employed. The critical minimum cutting pressure is defined as the pressure required to prod-nce a jet whose nozzle exit velocity is the critical minimum cutting velocity. Some typical values of critical velocities yand pressures are:

l Stando is defined as the distance between the exit end of the nozzle and the target.

l Sand measured by bulk volume; bentonite by weight.

In any particular instance the critical minimum cutting pressure for a particular fluid and target material may easily be determined by experiment, since at pressures below the critical value the jets do not appreciably cut the target rock whereas lonly at pressures above the critical value does any substantial cutting or penetration of the `drill occur. It is advantageous to substantially exceed the critical minimum cutting pressure and we prefer to use a pressure across the jet bits of this invention that exceeds about 4000 p.s.i. and have found it advantageous to operate with a pressure at tor above about 5000 p.s.i.

In this invention use is made of the fact that when a high velocity jet stream strikesa target at a low elevation angle (ie high angle of incidence as this term is used in optics) the jet is deviated to follow the target surface with little loss of momentum as a result of its change in direction. This means that a penciliform jet stream incident at a high angle of incidence on a target surface will stream substantially tangent to the surface of impingement with little reduction in velocity, the loss being only that due to the frictional effect of the target surface, which frictional effect at the high velocities employed results in cutting the target. This is in contrast to the behavior of a jet stream that strikes a target at near normal incidence in which case the large change in direction of the splash results in substantial l-oss of energy of the stream through impact so that the splash velocity is very much lower than the incident velocity. The jet drill bits of this invention utilize jets that strike the borehole wall at a high angle of incidence whereby the jet velocity is not diminished by excessively sudden change in direction of the jet stream. The jet bits of this invention thereby utilize the jets in a manner that substantially increases the cutting effect. At the same time the backsplash of the jet is controlled and directed to expend its energy against the target being cut before it again strikes the tool so that erosion of the bit itself is very materially reduced.

These effects are employed in this invention to provide high rates of target penetration. In the jet bits of this invention the-nozzles are so located and directed to produce jets that irnpinge on the borehole wall at a small angle with the tangent to the borehole wall at the point of impact, whereby the jet upon deflection a-t the borehole wall retains a substantial amount of its velocity and further erodes the borehole wall beyond the point of impact. Ancillary to the fact that the deflected jet parallels the borehole wall beyond the point of impact is the fact that the jets. do not strike the tool itself until Ithe jet energy is materially dissipated, thus substantially `avoiding erosion of the tool by backsplash.

IIn the jet bits used in this invention there are provided nozzles whose jets are directed generally downward to drill a pilot hole ahead of the main hole to be drilled. The bit is also provided with additional nozzles whose jets lare directed in such manner as to enlarge the pilot hole to main gauge. By means of such an arrangement of nozzles Ithe jet bits of this invention utilize the enlarging jets to maximum advantage thus achieving high penetration rates for the drill.

Referring first to FIGURES l to 3 which respectively show bottom, front, and side views of one embodiment of a jet drill bit useful in this invention, the body of the bit proper has the general shape of a truncated and flattened cone that is fastened to a shank 11 either by welding or forged integral therewi-th. The shank 11 is provided with conventional drill pipe threads (not shown) for removably attaching the bit to a conventional rotary drill pipe. The inside 12 of the body 10 is hollow and is in communication with the axial opening 13 of the shank and drill pipe in order that drilling fluid under high pressure may be supplied to the jets of the bit.

The body 10 of the bit is generally rectangular in cross section as -best seen in FIGURE 7. The two trailing edges of the body are provided with hard wear-resistant inserts 14 and 15 made, for example, of blocks of the material commercially available under the trade name Kennametal. The blocks 14 and 15 are welded or brazed onto the body 10. The body 10 is also provided with a plurality of nozzles to be described. The nozzles are made of hard wear-resisting material such as Kennametal. Each nozzle comprises a right circular cylinder about 1/2 inch long and about 3/8 inch in outside diameter. Each nozzle of FIGURES 1 to 7 has an axial opening which in the jet bits of this invention yis 1/s inch in diameter and has a conventional elliptical entrance portion as best seen in FIGURES 4 to 7.

The bottom end 16 of the body of the bit is substantially flat and is provided with a tongue 17 that extends a dis-tance beyond the end of the bit to provide standoff for a number of nozzles 18, 19, 20, 21, and 22. The leading edges of the tongue 17 are provided with hard wearresistant (e.g. Kennametal) inserts 23 and 24 welded or brazed thereon. It has been determined that the optimum standoff is between 1/2 inch and 11A inches and it is preferred that the length of the tongue as measured from the bott-om end 16 of the bit body be about l inch as disclosed and claimed in our copending coassigned application Ser. No. 311, 088. The nozzles 18 to 22 are inserted and brazed into holes 27 drilled in the bottom of the bit at appropriate locations and directions so that the nozzles are in communication with the interior 12 of the bit. The tongue 17 is recessed at 25 to provide clearance for insertion of nozzle 19 and for the jet issuing therefrom.

The nozzle 19 has its axis sugstantially parallel to the longitudinal axis 26 of the bit, and is located at the smallest radius from the axis. Nozzle 21 is located at a slightly larger radius from the axis 26 of the bit and is also directed outward at an angle, for example about 28.5, as best seen in FIGURE 5. The nozzle 21 is located and directed so that its jet impinges on the bottom of the hole being drilled at a radius that is one jet-produced groove width farther from the axis of the borehole than the point of impingement of the jet from nozzle 19. The nozzles 18, 2d, and 22 are each located at a corner of the bottom of the bit and are directed so as to cut a groove at the bottom of the borehole that is one jetproduced groove width farther from the axis of the borehole than the point of impingement of the jet from nozzle 21. Inasmuch as the radius of the point of impingement of the jets from nozzles 18, 2li, and 22 is lconsiderably larger than that of the nozzles 19 and 21, it is preferred to employ three such nozzles 18, 20, and 22, which are directed as best seen in FIGURE 6 to make an angle of, for example 22 with the axis of the bit. The arrangement of the impingement of the jets 18 to 22 on the bottom of the borehole is such as to achieve substantially uniform areal distribution of penetration rate on the bottom of the borehole as disclosed and claimed in copending, coassigned application Ser. No. 311,088. The standolf bar 17 thus needs only to smooth out minor ridges or irregularities that may remain on the bottom of the pilot hole drilled by the jets 18 to 22, but the standoff bar does no substantial mechanical cutting.

On the longer side of the rectangular section of the body 10 and close to the leading edges of the body there are provided a `plurality of nozzles 30, as for example five nozzles 30 on each side, as best seen in FIGURE 2. Each of the five side nozzles are of the same type as the bottom nozzles 18-22 and each has an j/6 inch exit opening. The side nozzles 30 are brazed or welded into holes 29 drilled in the body 10 and which provide communication from the nozzle to the interior of the bit. Each of the holes 29 into which the side nozzles 30 are mounted is drilled on a plane perpendicular to the axis 26 of the bit. Each hole 29 Amakes a high angle, as for example 70 with the adjacent flat face of the drill body as best seen in FIGURE 7. The location and direction of the respective side nozzles 30 is thus such that the emerging jets strike the borehole wall on the plane through the nozzle perpendicular to the axis of the borehole and make an angle with the tangent to the borehole wall at the point of impingement that varies somewhat with each nozzle, but is in the neighborhood of about 40 to 50. The angle of incidence (measured to the perpendicular to the target) is thus inthe range of 40 to 50. As a consequence of the high angle of incidence, the jet emerging from the nozzle substantially maintains its velocity after the first impact whereby the jet stream parallels the borehole wall for a substantial distance and effects a further cutting action. In this manner a maximum of hydraulic power is extracted from each of the side jets to obtain high cutting rates. It is further apparent that as the jet stream follows the borehole wall it is constrained to hug the wall because of the curved configuration lof the wall whereby the jet effectively scours the borehole wall meanwhile eroding the vrock formation being drilled so as to enlarge the local holle diameter thus permitting the generally tapered form of the bit to progress into the drilled hole. It is also apparent that the jet stream does not again strike the body of the bit until the stream has traversed nearly a semi-circumference .of the hole bywhich time the jet has been materially reduced in velocity so that upon again reaching the bit body the jet no longer has sufficient energy to appreciably cut the bit body. It is also seen that if the jets, after traversing the borehole wall strikel the bit body they strike on the Wear-resistant inserts 14 and 15 and these thus protect the bit body from erosion as well as removing any protrusions accidentally left by the jets.

FIGURES 8 to 21 show a second embodiment of the jet bit useful in this invention. This embodiment comprises a body portion 4l) having the shape of a truncated right square pyramid best seen in FIGURES 8, 9, and 10. The base of the body40 has a shank 41 that iscircular in section and has a central opening 42 (best seen in FIGURE 14) which communicates with the inside of the rotary drill pipe to which the tool is fastened. The shank 41 is provided with conventional drill pipe threads (not shown) by means of which the -tool is fastened to the drill pipe and rotated in conventional manner.

Each of two diametrically opposing leading corners 43 and 44 of the body 40 is provided with a bulge 45 and 46, respectively whose outer surface conforms to that of a portion of cone of substantially the same apex angle as the corners 43 and 44. Clearance is provided in the space between the trailing edge 47 and 48 of each bulge and the next following corner, the latter being respectively 49 and 50. The clearance between the trailing edges 47 and 4S and the next following corners `49 and 50 pro# vide space for ow of spent drilling fluid upward from the region of the nozzles to the annular space between the drill pipe and the borehole wall.

The apex (bottom) end of the drill bit is provided with openings 51, 52, and 53 that communicate with the inner opening 42 of the bit. Into each of the openings there is fastened as by brazing or welding a nozzle 54, 55, and 56 respectively, best seen in FIGURES 15 and 16. The openings 51, 52, and `53 may be provided with a shoulder as shown against which the respective nozzles abut in order to rmly hold the nozzle in place during the welding or brazing operation. Each nozzle, comprises a lright circular cylinder about 1/2 inch long and about 3A; inch in outside diameter and is made of wear-resistant material, such as Kennametal. Each nozzle of FIGURES 8 to 21 has an axial opening of Ms inch diameter with a conventional elliptical entrance portion as best seen in FIGURES 15 and 16. The openings 51, 52, and 53, and therefore also the respective nozzles 54, 55, and 56 are directed so as to impart the rock formation immediately below the bit at substantially zero standoff and at radii such as to deliver substantially uniform areal distribution of penetration rate to the rather limited (apex or pilot) area of the bottom of the borehole, as disclosed and claimed in coassigned, copending application Ser. No. 311,088. To this elect nozzle 54 points slightly toward the axis of the bit, nozzle 55 points slightly outward from the axis of the bit, and nozzle 56 points further outward from the axis substantially as indicated in FIG- URES l and 16. Thus the jets from nozzles 51 to 54 drill a pilot hole ahead of the main bit.

Returning again to FIGURE 8, each of the flat faces of the body 40, i.e. the flat face bounded by edges 43 and 50 and that bounded by edges 44 and 49, are provided wih a plurality of nozzles whose location can be best seen in FIGURES 10 and 11, respectively. In FIGURE 1l the nozzles 57, 58, 59, 60, 61, and 62 are brazed or welded into openings drilled in the bit body 40 on a plane perpendicular to the axis of the bit as best seen in FIGURE 13. The nozzles 57 to l62 are brazed in their respective openings, each of which has a slight shoulder against which the nozzle rests. The nozzles 57 to 60 of FIGURE 13 are all directed at substantially the same angle with respect Vto ythe radius to the axis of -the bit as best seen in FIGURES 19, and 21 and nozzles `61 and 62 at a somewhat less angle as indicated. Nozzle 57 is slightly smaller in outside diameter than the others because of the lack of space at the point of the bit. The inner end of each opening into which the nozzles 57 and 62 are mounted meets with a relief groove 63 to permit drilling Huid access from inside the bit to the nozzles.

Referring again to FIGURE 8, the flat face of the bit body bounded by edges 44 and 49 is provided with nozzles 64, 65, 66, 67, and 68 mounted by brazing into openings that are drilled at an angle to a transverse plane perpendicular to the axis of the bit. The nozzles are directed downward at an angle of substantially 45 as best seen in FIGURES 10 and 12. These nozzles are also directed at an angle of about 90 with respect to the radius to the axis of the bit as best seen in FIGURE 18. The inner end of the respective openings into which the nozzles 64 to 67 are mounted communicate with a groove 69 that permits drilling fluid access from inside the bit to the nozzles.

It is apparent from the location and directional orientation of the nozzles in the bit of FIGURES 8 to 21 that the angle of incidence of the jets issuing from nozzles 57 to 62 and 64 to 68 as measured with respect to the normal to a tangent plane at the point of impact will be large being in the range of 40 to 50. The jet upon deflection by the target surface thus is able to retain a substantial portion of its kinetic energy. The jet subsequently follows and, because of the curved Iconfiguration of the borehole wall, the jet hugs the borehole wall to scour the wall and effectively erode it to deepen and enlarge the hole. The downwardly directed jets 64 to 68 set up a violent swirling action of the fluid against the borehole wall that effectively erodes the conical end of the borehole to enlarge and deepen it. Furthermore, the jets expend most of their energy in contact with the borehole wall before again encountering the body of the bit thus materially reducing erosion of the bit body.

FIGURES 22 to 27 illustrate a third embodiment of a drill bit useful in this invention in which the jet bit has an elongated pilot drill that extends downward beyond the end of the main body of the drill. The pilot drill is provided with `downwa-rdly directed nozzles whose highvelocity jets drill the pilot hole ahead of the main hole to be drilled. In addition, the pilot drill is provided with nozzles in the side thereof whose jets cut away the shoulder at the top of the pilot hole and serve to enlarge the hole to main gauge. The latter jets are directed horizontally or at -a generally upwardly directed angle and thereby attack the rock being drilled in a direction of weakness, i.e. along the bedding planes, which results in a high rate of penetration of the drill.

Referring to FIGURES `22 to 27, this embodiment of drill bit comprises a tubular shank 110, best seen in FIGURES Z4 and 25, that is provided at its upper end with standard drill-pipe threads (not shown) 'by means of which the bit is attached to the conventional rotary drill stem. The bit is enlarged in diameter at 111 and if desired, the enlarged body portion 111 may be manufactured separately and shrunk and welded to the shank as shown at 112. The outer surface of the body 111 is provided with a plurality of utes 108, best seen in FIGURES 22 and 23. The bit has a shoulder at 114 to form a surface that is substantially perpendicular to the axis of the body 111. The axis 115 of the body of the lbit coincides with the axis of the drill pipe to which it is fastened. Extending from the surface 114 is a hollow cylindrical protuberance or nose 116 of reduced diameter that forms a pilot drill whose axis also coincides with the axis 11S of the body of the bit. The cylindrical portion of the nose 116 terminates with a surface 117 that is substantially perpendicular to the axis 115. The nose 116 has two ldiametrically opposed angled surfaces 122 and 123 whose intersection with the cylindrical surface of nose 116 forms the semi-elliptical outlines shown in FIGURES 24 and 25. The angled surfaces 122 and 123 need not be symmetrical with respect to the axis 115 of the bit, and in the bit illustrated surface 123 is somewhat closer to the axis than is the surface 122. The surfaces 122 and 123 are angled to run out just below the transverse shoulder 114. The outside diameter of the nose 116 is approximately one-half that of the body portion 111. The lower end of the nose is provided with a transverse extension 118 in the form of a tongue as best seen in FIG- URE 22. The tongue 118 extends transversely entirely across the surface 117 at the lower end of the pilot drill 116. The body of the bit has a central opening 120 which is reduced in diameter to 121 in the nose 116. The bore terminates at a substantially at inner surface 119 above the surface 117.

At the shoulder 114 two diametrically opposed lugs 124 and 125 are provided as best seen in FIGURES 24 and 25. The purpose of lugs 124 and 125 is to insure that the drilled borehole is to gauge and for this purpose the leading edges of lugs 124 and 125 are provided with hard metal surfacings 127 and 128 made, for example, of the material commercially available under the name of Kennametal, fastened the-reon as by brazing or welding and best seen in FIGURE 22. The hard surfacings 127 and 128 do no substantial cutting but serve merely to hold the hole to gauge and to break away any remaining protrusions that may accidentally be left by the hydraulic jets to be described.

The bit is provided with three `groups of nozzles indicated in FIGURES 26 and 27 generally by A, B, and C, respectively. The nozzles are in the form of right circular cylinders that are mounted in openings drilled in the bit as shown. Each of the nozzles of FIGURES 22 to 27 has a Central axial opening of 1/s inch diameter and whose inside end has a conventional elliptical contour in order that fluid from inside of the bit will flow into each nozzle in streamline fashion. The nozzles may be made of abrasion-resistant material, as for example the material commercially available under the trade name Kennametal. The holes in which the nozzles are mounted in the drill bit have locations and orientations to be described. The direction of the nozzle is defined as the direction of the emerging jet stream.

The group A of nozzles is located at the bottom end of the nose 116 forming the pilot drill. Group A cornprises four nozzles, two of which are located on each side of the tongue 118. The four nozzles, indicated as 130, 131, 132, and 133 are best seen in FIGURE 22. The nozzles are generally inclined with respect to the axis 115 of the bit, and are located to intersect the end surface 117 at various distances from the axis 115 as shown in FIGURE 22. One of the nozzles 133 is parallel to the axis 115, two of the nozzles 130 and 131 are inclined at an angle of 18 27 with respect to the axis of the bit, and nozzle 132 is directed at an angle of 8 with respect to the axis 115. All of the nozzles are directed so that their respective axes intersect the axis 115 of the bit except nozzle 133 whose axis is parallel to the axis 115. The nozzles 130, 131, and 132 are inclined so as to direct a jet with a radially outward component of velocity. The holes into which the respective nozzles are fastened are drilled at the desired angles through the lower end of the nose 116 to communicate with the inner bore 121 of the bit. The group A nozzles are located and oriented so that the jets issuing therefrom deliver to the bottom of the hole a substantially uniform areal distribution of penetration rate as previously explained in order that the drill will effect uniform penetration over the pilot hole area, thereby leaving little or no material to be removed by the tongue 18.

Group B of the nozzles comprises four nozzles fastened in openings drilled in the nose 116 substantially halfway between the bottom surface 117 and the shoulder 14. These nozzles are best seen in FIGURES 26 and 27 and are indicated by 135, 136, 137, and 138. Three of the nozzles 135, 137, and 138 are mounted in openings that are substantially the same axial distance from the surface 117, and nozzle 136 is placed in a hole started somewhat closer to the surface 117. Nozzle 135 is directed radially outward at right angles to the axis 115. Nozzle 137 is directed upward at an angle of 60 to the axis 115. Nozzle 138 is directed upward at an angle of 75 to the axis 115. Nozzle 136 is directed upward `at an angle of 45 to the axis 115. The axis of each of the nozzles intersects the axis 115 of the drill bit. It is apparent that whereas the nozzles 130, 131, 132, and 133 are directed downward, the nozzles 136, 137, and 138 are directed generally upward and nozzle 135 is directed radially outward. We have .found that best results are obtained when nozzle 135 is located in the range between and 1/2 inch below the lower edge of the lugs 124 and 125, i.e., when the dimension 148 in FIGURE 26 is in the range 0 to 1/2 inch.

Group C of the nozzles is best seen in FIGURES 22, 26, and 27 and comprises four nozzles 140, 141, 142, and 143. Nozzles 140, 141, and 142 are located on one side of the lugs 124 and 125, whereas nozzle 143 is located on the other side of the lugs as best seen in FIGURE 22. The holes for nozzles 140, 141, 142, and 143 are drilled at an angle of 20 with respect to the axis 115 and their respective axes intersect the axis 115. The nozzles 140, 141, and 142 are spaced 45 apart in azimuth about the axis 115, and nozzles 140 and 142 are spaced 45 from the transverse axis of lugs 124 and 125. Nozzle 143 is spaced 45 from the transverse axis of the lug 125. The nozzles of group C are directed outward to strike the shoulder formed in the rock at the top of the pilot hole at a radius equal to the outside radius of the main body of the drill. This is indicated as point 147 in FIGURE 26. Thus the group C jets cut the hole to size, assisted by the group B jets that cut Vout the shoulder between the pilot hole and the maingauge hole.

It is apparent that all of the nozzles are in communication with the central opening in the bit and they are supplied with pressurized drilling fluid pumped into the top of the 'bit stem in conventional manner at a pressure that is sufficient to produce jets whose velocity exceeds the critical minimum cutting velocity. The high velocity jets issuing from nozzles 130, 131, 132, and 133 impinge on the rock directly below the bottom of the pilot bit and the standoff of these nozzles is controlled by the axial height of the tongue 118. It is preferred that the standoff be in the range 1/2 inch to 1% inches as previously mentioned. As the bit is rotated, these jets affect disintegration of the rock below the nose 116.

The nozzles 135, 136, 137, and 138 produce jets that serve to enlarge the hole in the region proximately below the shoulder where the pilot hole enlarges to the main hole so as to make room for the enlarged body portion 111 of the bit. The nozzles 140, 141, 142, and 143 serve to further enlarge the hole to the main gauge and remove material below the lugs 124 and 125. The lugs 124 and 1215 serve to maintain proper standoff for jets 140, 141, 142, and 143. It is preferred that this standoff also be in the range 1/2 inch to 1% inches. The outer edges of the lugs 124 and 125 hold the gauge of the hole and remove any remaining rock protrusions.

It is apparent that when the drill is operating at the bottom of a deep hole there will be a transition in the hole where it enlarges from substantially the diameter of nose 116 to that of body 111, i.e. from pilot hole to main gauge hole. The group B jets 135, 136, 137, and 138 serve to effectively cut away this shoulder Vand thereby permit faster drilling. The group B jets are directed generally upward and this makes them particularly effective in removing material from this shoulder. The group B jets are directed at successively increasing angles to the axis 115, starting with nozzle 136 directed at 45 to the axis, nozzle 137 at 60, nozzle 138 at 75, and nozzle at 90. Therefore, as these jets rotate in the conventional clockwise manner, they successively cut the rock to an increasing angle to effectively cut down the shoulder of rock formed at the top of the pilot hole. Inasmuch as the rock layers in which drilling takes place are generally approximately horizontal and the rock layers are very weak in tension across the bedding planes, it is seen that the upwardly directed jets serve to pry loose akes or layers of rock and are very effective in enlarging the pilot hole to main gauge size.

The jet bits used in this invention are supplied with drilling fluid under a pressure at the surface exceeding about 4000 p.s.i., substantially all of which will exist as pressure differential across the nozzles effecting an exit velocity exceeding about 650 f.p.s. which exceeds the critical minimum cutting velocity for most rocks. This has been found to be effective in rapidly making hole in hard rock. It is preferred to employ drilling fiuid containing between about 5 percent and about 15 percent sand of size predominantly between about 20 mesh and 40 mesh in order to further increase the penetration rate of the bit as disclosed and claimed in copending, coassigned application Ser. No. 311,088.

Certain aspects of the invention herein disclosed are disclosed and claimed in our -copending applications Ser. No. 311,035 and Ser. No. 311,088, each filed of even date herewith and assigned to the same assignee as this application.

What we claim as our invention is:

1. A hydraulic jet method for drilling the borehole of a well through hard subsurface formations comprising delivering a drilling liquid having abrasive suspended therein downwardly through rotating drill pipe to a drilling tool secured to the lower end thereof, discharging downwardly from the drilling tool at a distance in the range of 1/2 inch to 11A inches above the bottom thereof a 'plurality of hydraulic jet streams of the drilling liquid located to cut a central pilot hole having a diameter less than the diameter of the borehole, discharging laterally from the drilling tool in a non-radial direction having a horizontal component a plurality of hydraulic jet streams of the drilling liquid to impinge against the Wall of the pilot hole at a high angle of incidence and enlarge the pilot hole to the desired borehole diameter, and lowering the drilling tool to maintain the lower end of the drilling tool against the bottom of the pilot hole and the distance between the bottom of the pilot hole and the level of discharge of the drilling liquid in the range of l/z inch to 1% inches, each of said jet streams having a velocity exceeding 650 feet per second.

2. A method as set forth in claim 1 which at least some of the laterally directed jet streams are discharged from the drilling tool at dilerent elevations, and each of the 12 laterally directed hydraulic jet streams is discharged from the drilling tool at a greater distance from the center of rotation of the drilling tool than any lower hydraulic jet stream.

References Cited UNITED STATES PATENTS 666,799 1/ 1901 Buckwalter 175-422 1,003,284 9/1911 Martin 175-422 2,218,130 10/1940 Court 175-422 2,518,591 8/1950 Aston et al. 175-422 2,758,653 8/1956 Desbrow 175--422 2,783,972 3/1957 Fehlmann 175-422 2,785,875 3/1957 Hayes 175-422 3,112,800 12/1963 Bobo 175-67 FOREIGN PATENTS 512,785 11/1930 Germany.

20 CHARLES E. OCONNELL, Primary Examiner.

I. A. LEPPINK, Examiner. 

1. A HYDRAULIC JET METHOD FOR DRILLING THE BOREHOLE OF A WELL THROUGH HARD SUBSURFACE FORMATIONS COMPRISING DELIVERING A DRILLING LIQUID HAVING ABRASIVE SUSPENDED THEREIN DOWNWARDLY THROUGH ROTATING DRILL PIPE TO A DRILLING TOOL SECURED TO THE LOWER END THEREOF, DISCHARGING DOWNWARDLY FROM THE DRILLING TOOL AT A DISTANCE IN THE RANGE OF 1/2 INCH TO 1 1/4 INCHES ABOVE THE BOTTOM THEREOF A PLURALITY OF HYDRAULIC JET STREAMS OF THE DRILLING LIQUID LOCATED TO CUT A CENTRAL PILOT HOLE HAVING A DIAMETER LESS THAN THE DIAMETER OF THE BOREHOLE, DISCHARGING LATERALLY FROM THE DRILLING TOOL IN A NON-RADIAL DIRECTION HAVING A HORIZONTAL COMPONENT A PLURALITY OF HYDRAULIC JET STREAMS OF THE DRILLING LIQUID TO IMPINGE AGAINST THE WALL OF THE PILOT HOLE AT A HIGH ANGLE OF INCIDENCE AND ENLARGE THE PILOT HOLE TO THE DESIRED BOREHOLE DIAMETER, AND LOWERING THE DRILLING TOOL TO MAINTAIN THE LOWER END OF THE DRILLING TOOL AGAINST THE BOTTOM OF THE PILOT HOLE AND THE DISTANCE BETWEEN THE BOTTOM OF THE PILOT HOLE AND THE LEVEL OF DISCHARGES OF THE DRILLING LIQUID IN THE RANGE OF 1/2 INCH TO 1 1/4 INCHES, EACH OF SAID JET STREAMS HAVING A VELOCITY EXCEEDING 650 FEET PER SECOND. 